Field of the Invention
The present invention relates to an optical integrated circuit.
Priority is claimed on Japanese Patent Application No. 2016-064858, filed on Mar. 29, 2016, the content of which is incorporated herein by reference.
Description of Related Art
In recent years, the amount of information transmitted by optical communication has increased. Measures, such as increasing the transmission rate and increasing the number of channels using wavelength multiplexing communication, have been taken in order to respond to an increase in the amount of information. In particular, in a next-generation 100-Gbps digital coherent transmission technique for achieving high-speed information communication, a polarization multiplexing system that transmits information in two polarization modes in which the electric fields are orthogonal to each other is used. In the polarization multiplexing system, the amount of information per unit time can be twice more than that in an optical transmission system using single polarization mode.
In an optical modulation system for high-speed communication including the polarization multiplexing system, an optical integrated circuit using a planar optical waveguide element has been developed in order to reduce a size or costs.
In particular, a technique has been improved which converts an incident optical wave in arbitrary polarization state and in single mode into an optical wave in specific linear polarization and performs optical signal processing in the planar optical waveguide element, in order to achieve a high-speed and high-capacity optical fiber network.
Japanese Patent No. 5319468 discloses a structure in which a degree-of-polarization monitor or an optical signal-to-noise ratio (OSNR) monitor is configured using an optical circuit formed by an interferometer and an arbitrary polarized optical wave of incident light is converted into a specific linearly polarized optical wave. In particular, in an optical circuit disclosed in Japanese Patent No. 5319468, a polarization beam splitter is provided in an optical branching section, different polarized optical waves are output to two arm waveguides, and a polarization rotator that rotates a polarization plane 90° is inserted into one of the arm waveguides.